Measurement of the associated production of a single top quark and a Z boson in pp collisions at $\sqrt{s}=$ 13 TeV

A measurement is presented of the associated production of a single top quark and a Z boson. The study uses data from proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded by the CMS experiment, corresponding to an integrated luminosity of 35.9 fb${}^{-1}$. Using final states with three leptons (electrons or muons), the tZq production cross section is measured to be $\sigma$(pp$\to$tZq$\to$Wb${\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}$q) = $123_{-31}^{+33}$ (stat) ${}_{-23}^{+29}$ (syst) fb, where $\mathrm{\ell }$ stands for electrons, muons, or $\tau$ leptons, with observed and expected significances of 3.7 and 3.1 standard deviations, respectively.